Process for the preparation of acyloxyalkanesulfonic acids

ABSTRACT

A fatty acid and/or an alkyl ester of a fatty acid and isethionic acid are allowed to react at a temperature of not more than 130° C. The present invention provides a process for preparing a fatty ester of isethionic acid or a salt thereof exhibiting an ameliorated hue and smell and in which few by-products are produced.

This application is a 371 of PCT/JP97/04467 filed on Dec. 5, 1997.

FIELD OF THE INVENTION

The present invention relates to a process for preparing an acyloxyalkanesulfonic acid and a salt thereof. More specifically, the inventionrelates to a process for preparing an acyloxy alkanesulfonic acid and asalt thereof wherein the acyloxy alkanesulfonic acid can be preparedunder mild conditions.

DESCRIPTION OF THE RELATED ART

Sodium salts of fatty esters of hydroxy alkanesulfonic acids such asisethionic acid (2-hydroxy ethanesulfonic acid) have far strongerresistance to hard water than soap, are mild to the skin and providelather with a rich body. They are also relatively thermoplastic whenused as a material for molding synthesized soaps or composite soaps. Dueto these characteristics, they have been used for a long time asmaterials for producing synthesized soaps or composite soaps, componentsof shampoos and body cleaning agents, fiber scouring agents or coloringaids and the like.

According to “HAPPI, 92, 1995”, PPG Industries, Inc. discovered that atroom temperature the water solubility of a salt of a coconut oil fattyester of isethionic acid was improved by 30% by changing the counter ionthereof from a sodium ion to an ammonium ion, and introduced the salt asan active agent which was mild, environmentally friendly and had goodlathering qualities. Generally, ammonium salts are known to have a watersolubility higher than that of sodium salts. However, there is adisclosure that the difference brought about by the ammonium salt of thecoconut oil fatty ester of isethionic acid is unprecedentedly large,that this salt has low peroral toxicity and is considered to be almostinnoxious, and that its biodegradability exceeds the OECD 301D guidelines, i.e. 65% in 15 days. Therefore, this substance is a surfactantwith great promise.

These salts of acyloxy alkanesulfonic acids, such as salts of fattyesters of isethionic acid are typically prepared as follows, whereisethionic acid is used as a representative example.

One such method is a process in which isethionic acid is allowed todirectly react with a fatty acid (U.S. Pat. No. 3,151,136, JapanesePatent Laid-open No.2-1454). In another method, a salt of isethionicacid produced in any process, for example, from a hydrogen sulfite suchas sodium hydrogen sulfite or ammonium hydrogen sulfite and ethyleneoxide, is esterified with a fatty acid (hereinafter referred to as adirect esterification method).

In the above-mentioned U.S. Pat. No. 3,151,136, a fatty acid is heatedto 100-120° C. under a reduced pressure, isethionic acid is then addedthereto and the mixture is maintained at 110° C., and then at 135° C. tocomplete the esterification reaction. In the Japanese Patent Laid-openNo.2-1454 discloses that isethionic acid and a fatty acid are reacted at110-120° C., then after-stirring is carried out at 135° C.

In Japanese Patent Laid-open No.2-1454, sodium salt of a fatty ester ofisethionic acid is produced from such materials as coconut oil fattyacid and isethionic acid. However, impurities are yielded as thereaction is carried out at a maximum temperature of up to 135° C., andthe obtained salt of the fatty ester of isethionic acid has low purityand shows deteriorated water solubility. This does not present a problemfor a salt such as a sodium salt which is not required to have highwater solubility, but for a salt which is required to have high watersolubility, this process is not practical.

Other examples employing the direct esterification method are given, forexample, in WO 95/01331 and WO 95/11957 wherein a process in whichammonium isethionate is produced from ammonium hydrogen sulfite andethylene oxide is described, and the obtained ammonium isethionate isused together with coconut oil fatty acid to produce an ammonium salt ofcoconut oil fatty ester of isethionic acid. In such a directesterification process, although sodium chloride is not a by-product,the reaction requires a temperature as high as almost 200° C., whichresults in yielding by-products, deterioration of hue and generation ofbad smell. Dehydration is carried out for the esterification reaction,however, as a lot of foaming occurs under a reduced pressure, thereaction takes a long time and a reaction vessel having a large capacityin relation to the amount of the product must be employed. There is noimprovement on this point in the process shown in WO 95/01331 and WO95/11957, since the main points thereof are to decrease the amount ofimpurities such as ethylene glycol during the production of salts ofisethionic acid.

An alternative method is a process in which an obtained isethionate saltand a fatty acid chloride are allowed to react to produce a fatty esterof isethionic acid (hereinafter referred to as acid chloride method). Inthis acid chloride method, the product can be obtained at a relativelylow temperature of not more than about 100° C., however, sodium chlorideis disadvantageously by-produced.

Furthermore, there is still another method in which an obtainedisethionate salt and a methyl ester of a fatty acid are subjected to anester exchange reaction (hereinafter referred to as ester exchangemethod). In this ester exchange method, again, a temperature as high asabout 200° C. is required for the reaction, therefore the problems ofby-products, deteriorated hue and generation of smell exist. Thisprocess is less advantageous from the view point of cost and ease ofoperation, since the production of a methyl ester of a fatty acid isinevitable.

The sodium salt of coconut oil fatty ester of isethionic acid haslimited uses due to its low water solubility, as an anionic surfactant,of up to several % at room temperature. Although the ammonium salt hasrelatively superior water solubility, it has a problem in that it smellsat higher pH ranges. Therefore, a salt of a fatty ester of isethionicacid having the same or a higher level of water solubility and latheringproperties has been desired. The industrially available hydrogen sulfitesalts are more or less limited to sodium and ammonium salts, and sincethe counter ion is not displaced in the production of an isethionatefrom a hydrogen sulfite salt and ethylene oxide or in the directesterification of an isethionate and a fatty acid, the types of counterions of the fatty ester of isethionic acid are more or less limited tosodium and ammonium. In order to produce a salt of a desired type, asodium salt or ammonium salt of a fatty ester of isethionic acid must besubjected to an ester exchange reaction and the like to be convertedinto the desired salt, thus it is not easy to industrially producevarious salts. Once a fatty ester of isethionic acid is obtained, it canbe neutralized with a desired counter base to industrially producevarious kinds of salts easily, and there is no need for an esterexchange reaction. Therefore, development of a process for preparing thefatty ester of isethionic acid has been long desired.

The purpose of the present invention is to provide a process ofpreparing an acyloxy alkanesulfonic acid or a salt thereof havingexcellent solubility in polar solvents, and salts of various counterions which can be easily produced therewith, wherein reaction is carriedout under mild conditions. Accordingly, few by-products are yielded, thehue and smell are ameliorated, there is little foaming and dehydrationof the reaction system under a reduced pressure can be easily carriedout so that the reaction time can be shortened, to provide a polarsolvent solution of the salt of the acyloxy alkanesulfonic acid.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a process for preparing anacyloxy alkanesulfonic acid from a fatty acid and/or an alkyl ester of afatty acid and a hydroxy alkylsulfonic acid is provided in which, anesterification reaction is carried out between the fatty acid and/or thealkyl ester of the fatty acid and the hydroxy alkylsulfonic acid at amaximum temperature of not more than 130° C.

In another aspect of the present invention, there is provided a processfor preparing a salt of acyloxy alkanesulfonic acid in which the acyloxyalkanesulfonic acid obtained by the above-mentioned process is allowedto react with a base.

In a further aspect of the present invention, there is provided asurfactant comprising a salt of an acyloxy alkanesulfonic acid obtainedby the above-mentioned process.

In yet a further aspect of the present invention, there is provided apolar solvent solution, emulsion, or dispersion of a salt of an acyloxyalkanesulfonic acid obtained by the above-mentioned processes.

BEST MODE FOR CARRYING OUT THE INVENTION

According to the present invention, a hydroxy alkyl group having 2-4carbon atoms is suitable as the hydroxy alkyl group of the hydroxyalkylsulfonic acid, and in particular, the best effect can be obtainedwhen the hydroxy alkylsulfonic acid is 2-hydroxy ethanesulfonic acid(isethionic acid). Accordingly, the present invention will be explainedusing isethionic acid as a representative example.

The process for preparing isethionic acid used as a raw material is notparticularly limited. For example, U.S. Pat. No. 4,910,330 discloses aprocess in which mercaptoethanol is oxidized, Japanese Patent Laid-opnNo.4-275,270 discloses a process in which sodium salt of isethionic acidis produced from sodium hydrogen sulfite and ethylene oxide, and sodiumis then removed by electrodialysis, U.S. Pat. No. 4,499,028 discloses aprocess in which dried sodium salt of isethionic acid is allowed toreact with concentrated hydrochloric acid, U.S. Pat. No. 4,696,773discloses a process in which isethionic acid is produced from a sodiumsalt of isethionic acid, hydrochloric acid and ethanol, U.S. Pat. No.5,053,530 discloses a process in which a sodium salt of isethionic acidand oxalic acid are allowed to react, and Japanese Patent Laid-openNo.3-66659 discloses a process in which isethionic acid is obtained froma sodium salt of isethionic acid, hydrochloric acid and ethanol. Atpresent, a process in which mercaptoethanol is oxidized with hydrogenperoxide is advantageous as it is an inexpensive process.

The presence of a compound such as ethylene glycol, which produces awater-insoluble product when esterified with a fatty acid willundesirably decrease the water solubility of a salt of a fatty ester ofisethionic acid and increase the clarifying temperature. In a processwherein mercaptoethanol is oxidized, oxidized intermediates such as2,2′-dithiodiethanol and a sulphoxide in which the S—S bond is retainedand oxygen is added present problems, and this content is preferably notmore than 1% based on a 70% aqueous solution of isethionic acid. Whenoxidizing mercaptoethanol, the use of an excess amount of an oxidizingagent for complete oxidation treatment can reduce the amount ofimpurities. In addition, these by-products can be removed and theproduct can be refined by ion-exchange treatment, adsorbing treatment,oxidation treatment, distillation, stripping and the like. For example,stripping can be carried out by blowing nitrogen gas at 50-100° C. under10-30 mmHg.

For preparing a salt of a fatty ester of isethionic acid, eitherisethionic acid alone or a mixture of isethionic acid and a salt ofisethionic acid can be used. The higher the ratio of the salt ofisethionic acid in the mixture of isethionic acid and the salt ofisethionic acid becomes, the higher the temperature required foresterification reaction becomes. Thus, in order to attain the object ofthe present invention it is desirable that the ratio of the salt ofisethionic acid is not more than 70%. Further, a replacement of thecounter ion does not occur, the type of counter ion of the isethionateis decided depending upon which type of isethionic acid fatty ester saltis desired.

A salt of isethionic acid can be obtained by partial neutralization ofisethionic acid with a base. The counter ion of the base used is notparticularly limited. For example bases in which an alkali metal ion(sodium, potassium, lithium and the like), alkaline earth metal ion(magnesium, calcium and the like), ammonium ion, alkanolamine ion(ethanolamine, diethanolamine, triethanolamine, isopropanolamine,diisopropanolamine, triisopropanolamine andethylenediaminetetra(propyleneglycol) and the like) are counter ions canbe used. The concentration and amount of the base are not particularlylimited. A salt of isethionic acid can also be synthesized from ahydrogen sulfite salt and ethylene oxide.

The fatty acid can be either a saturated or unsaturated fatty acid. Thenumber of carbon atoms of the fatty acid is 6-22, particularlypreferably 8-18. Examples include coconut oil fatty acid, palm kerneloil fatty acid, lauric acid, oleic acid, stearic acid, isostearic acidand the like. An alkyl ester of a fatty acid can be an alkyl ester ofeither a saturated or unsaturated fatty acid. The number of carbon atomsof the fatty acid is 6-22, particularly preferably 8-18. Examplesinclude coconut oil fatty acid, palm kernel oil fatty acid, lauric acid,oleic acid, stearic acid, isostearic acid and the like. The alkyl groupbonded thereto by ester linkage is not particularly limited, and methylor ethyl group can be used.

The molar ratio of a fatty acid and/or an alkyl ester of a fatty acid tothe isethionic acid and/or a salt thereof charged for esterification ispreferably 0.95-1.1. If this ratio is more than 1.1, a fatty acid and/oran alkyl ester of the fatty acid is left after esterification or a waterinsoluble esterified compound is produced, resulting in a decrease inthe water solubility of the neutralized salt and an increase in theclarifying temperature of the aqueous solution. If the ratio is lessthan 0.95, the esterification is incompletely carried out and this isdisadvantageous.

Although a catalyst is not usually required for esterification ofisethionic acid and/or a salt thereof and a fatty acid and/or an alkylester of a fatty acid, previously adding a fatty ester of isethionicacid and/or a salt thereof is preferable, because the reaction time canbe shortened.

Since the isethionic acid and/or a salt thereof are typically obtainedin the form of an aqueous solution, in the initial stage of theesterification of the isethionic acid and/or a salt thereof and a fattyacid and/or an alkyl ester of a fatty acid, they are not mutuallysoluble and a two phase non-homogeneous reaction is carried out, and thesystem becomes homogeneous as the reaction progresses and a fatty esterof isethionic acid or a salt thereof is generated. When an appropriateamount of a fatty ester of isethionic acid or a salt thereof is addedprior to esterification, the system becomes homogeneous from the initialstage of the reaction and the reaction time can be advantageouslyshortened. The amount of the fatty ester of isethionic acid or a saltthereof to be added is preferably 5-20% of the total amount of theisethionic acid and/or the salt thereof and the fatty acid and/or thealkyl ester of the fatty acid. If the amount is smaller than this rangea homogeneous system cannot be provided, while an amount greater thanthis range is disadvantageous in terms of cost. The esterificationreaction is progressed by heating the charged mixture of isethionic acidand/or the salt thereof and the fatty acid and/or the alkyl ester of thefatty acid to the reaction temperature followed by dehydration under areduced pressure.

The reaction temperature is 50-130° C., preferably 60-120° C. A reactiontemperature higher than this range is unnecessary or even undesirabledue to side reactions, staining or smell. At a temperature lower thanthis range, the reaction rate is slowed or the reaction does notproceed. Throughout the entire esterification reactions, the maximumtemperature is not more than 130° C., preferably less than 100° C. At atemperature higher than this, side reaction, staining or a smell occursand the object of the present invention cannot be achieved. According tothe process of the present invention, the reaction can be carried out ata low temperature and this is thought to be because the isethionic aciditself works as a catalyst.

According to the present invention, reduction of the pressure is notvery restricted as little foaming occurs. Therefore, the water generatedby esterification or the water existed as the solvent can be removedquicker and under a reduced pressure lower than the conventionalprocess. Accordingly, the reaction can be completed in a shorter timethan with the conventional process, and more importantly, the generationof by-products is controlled and a fatty ester of isethionic acid havingbetter water solubility than that of the conventional process can beobtained.

According to the present invention, an esterification reaction rate of90% or higher can be achieved as shown in the Examples.

When producing a salt of a fatty ester of isethionic acid, the productis allowed to react with a desired base after the esterification. Insuch an event, the produced ester is hydrolyzed if it is contacted withwater in an acid or alkaline condition at a high temperature and for along period of time, and since the polar solvent solution becomes turbidand the clarifying temperature is increased, it is preferable that apolar solvent solution of the base be added and the solution be stirredso that a high pH region is not locally generated. The polar solvent isnot particularly limited. For example, water, lower alcohols, glycols,and glycerin or a mixture thereof can be used. The final pH is adjustedto 6-8, preferably to 6.5-7.0 in order to prevent hydrolysis of theester linkage.

The counter ion of the base used is not particularly limited. Forexample, bases in which an alkali metal ion (sodium, potassium, lithiumand the like), alkaline earth metal ion (magnesium, calcium and thelike), ammonium ion, alkanolamine ion (ethanolamine, diethanolamine,triethanolamine, isopropanolamine, diisopropanolamine,triisopropanolamine and ethylenediaminetetra(propyleneglycol) and thelike) are counter ions, can be used. An alkanolamine salt obtained fromthe base in which alkanolamine is contained as the counter ion showsmuch better blending properties, lathering properties, water solubility,and sensation upon use than those of sodium salt and ammonium salt. Inparticular, the alkanolamine salt has good water solubility and itsviscosity in aqueous solution is much lower than that of the ammoniumsalt. Further, it has good blending properties with other active agents.The viscosity of the aqueous solution of the alkanolamine is increasedby addition of a sodium compound and the like which originally has a lowwater solubility, so the viscosity of the aqueous solution can be easilyadjusted. The concentration and amount of the base used are notparticularly limited.

When an aqueous solution of the produced fatty ester of isethionic acidor a salt thereof has problems such as staining and bad smells,sometimes treatment with hydrogen peroxide is effective. For example,the staining and smells can be ameliorated by adding 30% hydrogenperoxide to an aqueous solution of a salt of a fatty ester of isethionicin an amount of 0.01-1% followed by treatment at 50-100° C.

The obtained fatty ester of isethionic acid can be used for producing asalt of isethionic ester or as a reforming agent for various kinds ofresins. The obtained salt of the isethionic acid fatty ester can be usedfor the same uses as those of the conventional processes. That meansthey can be used in various uses as an anionic surfactant. For example,they can be dissolved in a polar solvent, emulsified or dispersed toprovide a synthesized soap, composite soap, shampoo, total body cleaningagent, fiber scouring agent, dyeing aid, rust proofing agent, lubricant,or resin reforming agent and the like. In particular, a salt ofalkanolamine or ammonium salt are useful as main components in shampoos,and body cleaning agents. In the former case, the product shows improvedblending properties, lathering properties and sensation after use,compared to products produced with the sodium salt.

EXAMPLES

The present invention will now be further illustrated by the followingexamples, however, the present invention is not limited to theseexamples so long as they do not exceed the essential features of thepresent invention.

Analysis of the reaction was conducted by a ¹H-NMR method. That is tosay, in the case of a fatty acid, signal of a methylene group adjacentto carbonyl carbon appears at δ2.22 ppm, while in the ester of thesignal of a methylene group adjacent to carbonyl carbon appears at δ2.29ppm. Therefore, the degree of conversion of a fatty acid was obtainedfrom a sample dissolved in dimethyl sulfoxide (DMSO) by measuring theintensity of the signal at δ2.22 ppm and that at δ2.29 ppm using aJNM-LA400 type F-NMR apparatus produced by JEOL Ltd., and by calculatingthe intensity ratio of these signals. As for the degree of conversion ofisethionic acid, since the signal of a methylene group adjacent to asulfonate group appears at δ2.72 ppm in the isethionic acid, and atδ2.82 ppm in the ester, and the signal of a methylene group adjacent tooxygen atom appears at δ3.69 ppm (isethionic acid) and at δ4.24 ppm(ester), the degree of conversion of isethionic acid was obtained fromthe intensity ratio of these signals and a mean value was calculated.

The by-produced 2,2′-dithiodiethanol and the sulfoxide thereof weredetermined by a standard addition method using ¹³C-NMR and the sulfuricacid was determined by ion chromatography.

The polar solvent (water) solution of each salt of the fatty ester ofisethionic acid was cooled until turbidity was observed, and thengradually reheated and the temperature at which the solution becametransparent (clarifying temperature) was obtained by visual observation.The hue was inspected by visual observation. The smell was examined byan organoleptic test. The viscosity was measured using B typeviscometer. Foaming properties were examined with a 0.2% aqueoussolution at 50° C. by the Ross-Miles method.

In Table 1, the terms “immediately after” and “5 minutes after” meanthat the foaming properties were measured “immediately after” and “5minutes after” the preparation of a 0.2% aqueous solution of a saltwhich had been obtained by adding a base and water listed in each of theTables. The unit of value is the height in mm of the foam.

Example 1

(1) 71.5% isethionic acid aqueous solution was obtained by oxidizingmercaptoethanol with hydrogen peroxide. The total amount of2,2′-dithiodiethanol and a sulfoxide thereof obtained as by-products was0.7%. The amount of sulfuric acid was 0.1%. Then 127 g of this 71.5%isethionic acid aqueous solution (0.72 mol of isethionic acid) and 144 g(0.72 mol) of lauric acid (neutralization value of 280 mgKOH/g) wereadded to a four-necked flask and heated under nitrogen stream to 100° C.This mixture was maintained at 100° C. for 30 minutes, and then thepressure was gradually reduced while taking the foaming state intoconsideration. There was little foaming, and it was possible to reducethe pressure from a normal pressure to 10-30 mmHg over about 30 minutesfrom the start of the pressure reduction. The water as the solvent andthe water generated by esterification were removed under a reducedpressure of 10-30 mmHg for 2 hours to give a lauric ester of isethionicacid of the present invention.

The esterification reaction rate of the fatty acid in this example was98%, and the esterification reaction rate of the isethionic acid was97%.

(2) To the obtained reaction product, was added each base shown in Table1 (Examples 1a-1h) and water such that the pH became 6.5 and the solidconcentration became 30% to give an aqueous solution of each salt oflauric ester of isethionic acid of the present invention. The results ofthe measurements of the clarifying temperature, hue, smell and foamingproperties of these products together with the bases added are shown inTable 1.

TABLE 1 Clarifying Hue Foaming property (mm) temperature APHAImmediately 5 min Example Base (° C.) No Smell* after after 1a 28%ammonia aq. soln. 15 150 ± 212 212 1b Ethanolamine aq. soln. 5 or below140 ± 223 223 1c Triethanolamine aq. soln. 5 or below 130 ± 221 220 1dIsopropanolamine aq. soln. 5 or below 140 ± 232 232 1eTriisopropanolamine aq. soln. 5 or below 140 ± 220 220 1fEthylenediaminetetra 5 or below 130 ± 230 230 (propylenegycol) aq. soln.1g Sodium hydroxide aq. soln. gelled — ± 212 204 1h Potassium hydroxideaq. soln. gelled — ± — — *Criteria for evaluation of smell ++: sensedstrongly +: sensed ±: barely sensed —: not sensed

Example 2

(1) 127 g of 71.5% isethionic acid aqueous solution (0.72 mol ofisethionic acid) used in Example 1, 157 g (0.72 mol) of coconut oilfatty acid (neutralization value of 257 mgKOH/g) and 28 g of previouslysynthesized fatty ester of isethionic acid (10% based on the aqueoussolution) were added to a four-necked flask. The mixture becamehomogeneous when stirred. The mixture was heated under a nitrogen streamto 80° C. and immediately after it reached 80° C., the pressure wasgradually reduced while taking the foaming state into consideration.There was little foaming and it was possible to reduce the pressure fromthe normal pressure to 10-30 mmHg over about 30 minutes from the startof the pressure reduction. The water as the solvent and the watergenerated by esterification were removed under a reduced pressure of10-30 mmHg for 3 hours to give a coconut oil fatty ester of isethionicacid.

Foaming during the dehydration reaction under the reduced pressure wasmuch less than in the case of the after-mentioned Comparative Example 1,and the operation was able to be carried out easily. The esterificationreaction rate of coconut oil fatty acid obtained from the reactionproduct by ¹H-NMR method was 95%, the esterification reaction rate ofisethionic acid was 95%.

(2) Then to the reaction product, was added each base shown in Table 2(Examples 2a-2g) and water such that the resulting pH became 6.6 and thesolid concentration became 31% to give an aqueous solution of each saltof coconut oil fatty ester of isethionic acid of the present invention.These were stained to some extent, and thus 30% hydrogen peroxide wasadded in an amount of 0.4% based on the aqueous solution and subjectedto treatment at 80° C. The results of the measurements of the productsobtained after the treatment together with the bases added are given inTable 2.

TABLE 2 Clarifying Hue Foaming property (mm) temperature APHAImmediately 5 min Viscosity Example Base (° C.) No Smell after after cPs2a 28% ammonia aq. soln. 15 250 ± 219 218 570  2b Ethanolamine aq. soln.5 or below 240 ± 224 224 9 2c Triethanolamine aq. soln. 5 or below 230 ±224 224 8 2d Isopropanolamine. aq. soln. 5 or below 240 ± 228 228 10  2eTriisopropanolamine aq. soln. 5 or below 240 ± 225 225 6 2fEthylenediaminetetra 5 or below 230 ± 227 227 6 (propyleneglycol) aq.soln. 2g Sodium hydroxide aq. soln. gelled — ± 216 216 —

Example 3

(1) 74.5% isethionic acid aqueous solution was obtained by oxidizingmercaptoethanol with hydrogen peroxide. The by-produced2,2′-dithiodiethanol and a sulfoxide thereof was 1.3%, and sulfuric acidwas 0.3%. The isethionic acid aqueous solution was subjected tostripping with nitrogen at 100° C. under 10-30 mmHg for 2 hours. To 122g of this 74.5% isethionic acid aqueous solution (0.72 mol of isethionicacid) obtained after the stripping treatment, was added 144 g (0.72 mol)of lauric acid and the mixture was heated under nitrogen stream to 100°C. The mixture was maintained at 100° C. for 30 minutes, and then thepressure was gradually reduced while taking the foaming state intoconsideration. There was little foaming, and it was possible to reducethe pressure from a normal pressure to 10-30 mmHg over about 30 minutesfrom the start of the pressure reduction. The water as the solvent andthe water generated by esterification were removed under a reducedpressure of 10-30 mmHg for 2 hours to give a lauric ester of isethionicacid.

The esterification reaction rate of the lauric acid obtained by ¹H-NMRanalysis of these reaction product was 95%, and the esterificationreaction rate of the isethionic acid was 95%.

(2) To the obtained reaction product, were added a 28% ammonia aqueoussolution and water such that the pH became 6.7 and the solidconcentration became 32% to give an aqueous solution of ammonium salt oflauric ester of isethionic acid of the present invention. The clarifyingtemperature of the aqueous solution was 20° C.

Example 4

(1) 127 g of 71.5% the isethionic acid aqueous solution (0.72 mol ofisethionic acid) used in Example 1, 225 g (0.79 mol) of oleic acid(neutralization value of 197 mgKOH/g) and 35 g of (previouslysynthesized) oleic ester of isethionic acid (10% based on the aqueoussolution) were added to a four-necked flask. The mixture becamehomogeneous when stirred. The mixture was heated under a nitrogen streamto 70° C. and immediately after it reached 70° C., the pressure wasgradually reduced while taking the foaming state into consideration.There was little foaming and it was possible to reduce the pressure fromthe normal pressure to 10-30 mmHg over about 30 minutes from the startof the pressure reduction. The water as the solvent and the watergenerated by esterification were removed under a reduced pressure of10-30 mmHg for 4 hours to give an oleic ester of isethionic acid.

The esterification reaction rate of oleic acid obtained by ¹H-NMRanalysis of these reaction product was 93%, and the esterificationreaction rate of isethionic acid was 90%.

(2) Then to the reaction product, were added a 28% ammonia aqueoussolution and a water-ethanol (4:1) solution to give a water-ethanol(4:1) solution of ammonium salt of oleic ester of isethionic acid of thepresent invention.

Example 5

(1) To 127 g of the 71.5% isethionic acid aqueous solution (0.72 mol ofisethionic acid) used in Example 1, was added 22 g of 28% ammoniaaqueous solution (0.36 mol) with cooling for neutralization and a 50%ammonia neutralized product of isethionic acid was obtained. Then of 150g (0.75 mol) of lauric acid was added thereto and the mixture was heatedunder nitrogen stream to 120° C. After the mixture reached 120° C., thepressure was gradually reduced while taking the foaming state intoconsideration. There was little foaming and it was possible to reducethe pressure from a normal pressure to 10-30 mmHg over about 30 minutesfrom the start of the pressure reduction. The water as the solvent andthe water generated by esterification were removed under a reducedpressure of 10-30 mmHg for 2 hours to give a partial ammonium salt of alauric ester of isethionic acid. The esterification reaction rate oflauric acid obtained by ¹H-NMR analysis of the reaction product was 94%,and the esterification reaction rate of isethionic acid was 97%.

(2) Then, to the reaction product, were added a 28% ammonia aqueoussolution and water such that the pH became 6.7 and the solidconcentration became 31%, to give an aqueous solution of ammonium saltof lauric ester of isethionic acid. The clarifying temperature of theaqueous solution was 17° C. The hue was APHA No. 150.

Comparative Example 1

To 122 g (0.69 mol) of the 71.5% isethionic acid aqueous solution usedin Example 1, was added 42 g of 28% ammonia aqueous solution (0.69 mol)and the pH was adjusted to 5 to give an ammonium salt of isethionicacid. To this mixture, were added 151 g (0.69 mol) of the coconut oilfatty acid used in Example 2, 0.25 g of methanesulfonic acid as acatalyst, and 0.42 g of hypophosphorous acid, and the mixture was heatedto 130° C. under nitrogen stream and the pressure was gradually reducedwhile taking the foaming state into consideration. vigorous foamingoccurred and it was difficult to reduce the pressure below 140-150 mmHgeven 60 minutes after the start of the pressure reduction and it took 10hours for the pressure to reach 10-30 mmHg.

Comparative Example 2

An ammonium salt of isethionic acid, coconut oil fatty acid,methanesulfonic acid, and hypophosphorous acid were mixed in a mannersimilar to that used in Comparative Example 1, and the mixture washeated to 170° C. under nitrogen stream and the pressure was graduallyreduced while taking the foaming state into consideration. Vigorousfoaming occurred and it was difficult to reduce the pressure below140-150 mmHg even 60 minutes after the start of the pressure reduction.The reaction was continued for 5 more hours at a reduced pressure ofaround 100-140 mmHg. The water generated was removed under a reducedpressure of 100-140 mmHg for 3 hours and an ammonium salt of coconut oilfatty ester of isethionic acid was synthesized. The esterificationreaction rate of coconut oil fatty acid obtained by ¹H-NMR analysis ofthe reaction product was 83%.

Then 28% ammonia aqueous solution and water were added to the reactionproduct such that the pH became 6.9 and the solid content became 32%,and 30% hydrogen peroxide was added in an amount of 0.1% based on theaqueous solution and the mixture was subjected to treatment at 60° C.for 3 hours. The results obtained after the treatment are shown in Table3. The hue of the aqueous solution was Gardner No.5, and the hue and thesmell were ameliorated by the treatment to some extent, however, the huewas inferior and the smell was stronger than those of Example 2. Theprocess of the present invention provides a better hue and smell asshown by comparison with this Comparative Example.

TABLE 3 Clarifying temperature Base (° C.) Hue Smell Example 2a 28%ammonia aq.soln, 13 APHA No250 ± Com- parative Example 2 28% ammoniaaq.soln, 60 or above Gardner No5 + + 3 28% ammonia aq.soln, 60 or aboveGardner No5 + + 4 28% ammonia aq.soln, 60 or above Gardner No4 + +

Comparative Example 3

122 g (0.72 mol) of the 74.5% isethionic acid aqueous solution used inExample 3 and 166 g (0.76 mol) of coconut oil fatty acid were added to afour-necked flask and heated under a nitrogen stream to 160° C. Afterreaching 160° C., the pressure was gradually reduced and the watergenerated was removed under a reduced pressure of 10-30 mmHg bydistillation and a coconut oil fatty ester of isethionic acid wassynthesized. The esterification reaction rate of coconut oil fatty acidobtained by ¹H-NMR analysis of the reaction product was 84%. A 28%ammonia aqueous solution and water were added to the reaction productsuch that the pH became 6.7 and the solid content became 31% to adjustthe aqueous solution. The clarifying temperature of the aqueous solutionwas over 60° C. and the hue of the aqueous solution was Gardner No.5. Asshown by comparison with this Comparative Example, the process of thepresent invention provides excellent hue and smell.

Comparative Example 4

157 g (0.72 mol) of coconut oil fatty acid was heated to 110° C. andbrought under a reduced pressure (50-70 mmHg) by use of water jet vacuumpump. Then, 127 g (0.72 mol) of the 71.5% isethionic acid used inExample 1 was added thereto dropwise and the mixture was stirred at 110°C. for 30 minutes and at 135° C. for 30 minutes while the solvent andthe water resulting from reaction were removed by evaporation to give afatty ester of isethionic acid. Foaming during the dehydration reactionunder a reduced pressure was nearly the same level as that of eachExample, but the esterification reaction rate of the coconut oil fattyacid obtained by ¹H-NMR analysis of the reaction product was 79%.

To the obtained reaction product, was added a 28% ammonia aqueoussolution and water such that the resulting pH became 6.8 and the solidconcentration became 32% to give an ammonium salt of coconut oil fattyester of isethionic acid. The obtained aqueous solution had a clarifyingtemperature of over 60° C. and a hue of Gardner No.4. As shown bycomparison with this Comparative Example the process of the presentinvention provides excellent clarifying temperature and hue.

INDUSTRIAL APPLICABILITY

The present invention provides a process of preparing a fatty ester ofisethionic acid or a salt thereof, and a polar solvent solution of thesalt of the fatty ester of isethionic acid, having excellent solubilityin polar solvents, and salts of various counter ions can be producedtherewith, wherein reaction is carried out under mild conditions andaccordingly few by-products are yielded, the hue and the smell areameliorated, little foaming occurs and since the dehydration of thereaction system under a reduced pressure can be carried out easily, thereaction time can be shortened.

What is claimed is:
 1. A process for preparing a salt of acyloxyalkanesulfonic acid, comprising: reacting a fatty acid and/or an alkylester of a fatty acid and a hydroxy alkylsulfonic acid in anesterification reaction at a maximum temperature of not more than 130°C., thereby providing an acyloxy alkanesulfonic acid; reacting saidacyloxy alkanesulfonic acid with ethylenediamine tetra(propyleneglycol).2. The process according to claim 1, wherein the esterification reactionis carried out at a reduced pressure of not more than 30 mmHg.
 3. Theprocess according to claim 1, wherein said hydroxy alkylsulfonic acid is2-hydroxy ethanesulfonic acid.
 4. The process according to claim 1,wherein a molar ratio of said fatty acid and/or said alkyl ester of saidfatty acid to said hydroxy alkylsulfonic acid is from 0.95 to 1.1. 5.The process according to claim 1, further comprising adding a fatty acidester of 2-hydroxy alkanesulfonic acid or a salt thereof which isprepared beforehand before said reacting of said fatty acid and/or alkylester of a fatty acid and said hydroxy alkylsulfonic aczid.
 6. Theprocess according to claim 1, wherein said reacting with ethylenediaminetetra(propyleneglycol) is carried out in a polar solvent.
 7. The processaccording to claim 6, wherein said polar solvent is selected from thegroup consisting of water, a lower alcohol, a glycol, glycerin andmixtures thereof.
 8. The process according to claim 6, wherein saidpolar solvent has a pH of 6 to
 8. 9. A water soluble salt of an acyloxyalkanesulfonic acid obtained by the process according claim
 1. 10. Asurfactant, comprising: a salt of an acyloxy alkanesulfonic acidobtained by the process according claim
 1. 11. A polar solvent solution,emulsion or dispersion of a salt of an acyloxy alkanesulfonic acidobtained by the process according claim
 1. 12. A process for preparing asalt of an acyloxy alkanesulfonic acid, comprising: reacting a fattyacid and/or an alkyl ester of a fatty acid and a hydroxy alkylsulfonicacid in an esterification reaction at a maximum temperature of not morethan 130° C., thereby providing an acyloxy alkanesulfonic acid; reactingsaid acyloxy alkanesulfonic acid with a base in water, glycerin or acombination thereof.
 13. The process according to claim 12, wherein theesterification reaction is carried out at a reduced pressure of not morethan 30 mmHg.
 14. The process according to claim 12, wherein saidhydroxy alkylsulfonic acid is 2-hydroxy ethanesulfonic acid.
 15. Theprocess according to claim 12, wherein said base is an alkanol amine.16. The process according to claim 15, wherein said alkanol amine isethylenediamine tetra(propyleneglycol).
 17. The process according toclaim 12, wherein said water, glycerin or said combination thereof has apH of 6 to
 8. 18. A water soluble salt of an acyloxy alkanesulfonic acidobtained by the process according claim
 12. 19. A surfactant,comprising: a salt of an acyloxy alkanesulfonic acid obtained by theprocess according claim
 12. 20. A polar solvent solution, emulsion ordispersion of a salt of an acyloxy alkanesulfonic acid obtained by theprocess according claim
 12. 21. A process for preparing an acyloxyalkanesulfonic acid, comprising: reacting a fatty acid and/or an alkylester of a fatty acid and a hydroxy alkylsulfonic acid in anesterification reaction at a maximum temperature of not more than 130°C., in the presence of a fatty acid ester of 2-hydroxy alkanesulfonicacid or a salt thereof which is prepared beforehand.
 22. The processaccording to claim 21, wherein said fatty acid ester of 2-hydroxyalkanesulfonic acid or said salt thereof is added in an amount of 5-20%based on the total weight of said fatty acid and/or alkyl ester of saidfatty acid and said hydroxy alkylsulfonic acid.
 23. The processaccording to claim 21, wherein the esterification reaction is carriedout at a reduced pressure of not more than 30 mmHg.
 24. The processaccording to claim 21, wherein the hydroxy alkylsulfonic acid is2-hydroxy ethanesulfonic acid.
 25. A process for preparing a salt ofacyloxy alkanesulfonic acid comprising: reacting the acyloxyalkanesulfonic acid prepared according to the process of claim 21 with abase.
 26. The process according to claim 25, wherein said base is analkanol amine.
 27. The process according to claim 26, wherein saidalkanol amine is ethylenediamine tetra(propyleneglycol).
 28. The processaccording to claim 25, wherein said reacting with said base is carriedout in a polar solvent.
 29. The process according to claim 28, whereinsaid polar solvent has a pH of 6 to
 8. 30. The process according toclaim 28, wherein said polar solvent is selected from the groupconsisting of water, a lower alcohol, a glycol, glycerin and a mixturethereof.
 31. A water soluble salt of acyloxy alkanesulfonic acidobtained by the process according to claim
 25. 32. A surfactant,comprising: a salt of an acyloxy alkanesulfonic acid obtained by theprocess according to claim
 25. 33. A polar solvent solution, emulsion ordispersion of a salt of an acyloxy alkanesulfonic acid obtained by theprocess according to claim 25.